That 14 day refund window is the tell, real courses give you way longer.

Bet that tube lasted longer than any kit too.

Did you check the moisture content on that white oak before you cut it? I read a piece from a woodworking mag a while back that said biscuits can wick moisture out of the glue and swell up, and if your slots are cut tight that swell has nowhere to go but into the joint line. Sounds like exactly what bit you. Titebond III is good glue but it does not fix a design that fights itself. The guys who say biscuits are just for alignment are right in theory, but in the real world a swollen biscuit can win the tug of war. Floating tenons give the glue room to do its job without the biscuit pushing back. You are not wrong, and the redo proves it.